This invention relates generally to using a remotely located device for cutting holes. More specifically, this invention relates to a method and apparatus for cutting through a liner in a conduit in order to re-establish service to lateral (incoming) lines.
It is well known that conduits that hold water sewage require repair due to leaking. This leakage may result from improper installation, deterioration due to aging, corrosive material running through the conduit, improper care, earth vibrations or other causes.
Typical leakage has been corrected by running a liner through a conduit as disclosed in U.S. Pat. Nos. 4,009,063 and 4,067,211. After the conduit has been lined, a cutter such as the ones disclosed in U.S. Pat. Nos. 4,648,454, 4,197,908, 4,701,988 or 4,422,891, is fed into the conduit to cut holes at the conduit's junctions.
These cutters have a cutter head disposed at one end and a motor that is connected to a carriage at the other end. The cutter turns rapidly while moving upward to cut a hole through the liner. A drawback to these cutters is that the cutter head may wobble while cutting, resulting in an inaccurate cut. Further, the cutter heads may not be able to exert enough force to cut away obstacles that protrude into the hole after the liner has been cut.
The locations of the junctions where the holes in the liner are to be cut may be located on the sides of the conduit. Further, the size of the hole may be large. Consequently, when the aforementioned cutters are used, they must be twisted and turned to place the cutting head in the proper orientation to cut the hole. The aforementioned cutters may not have the range of motion to cut large holes without having to stop cutting the liner, physically moving the cutter. Twisting and moving the cutters to reposition the cutting heads increases the time to cut holes in the liner which allows blocked lateral (incoming) lines to backup and possible overflow or backflow.
Another drawback to the cutters disclosed in the aforementioned patents is that they are constructed with many moving components. Except for the cutting head, prior art components are sealed in a cover to prevent contact with debris. However, debris may still seep through cracks around the cover resulting in the cutter's components corroding, thereby reducing its life expectancy.
Due to the tight space requirements of a conduit, the cutter's components must be compacted into a small region. When cutting it is desirable to cut deeply through the liner to cut away any debris or growth present in the junction. A drawback of the aforementioned cutters is that they may not have the extent of movement to allow the cutters to cut growth in the junction.
The devices described in the aforementioned patents use brakes which are connected through rams to the cutter's support structure. During operation the rams expand outward. This expansion results in the brake being pushed against the side of the liner to hold the support structure in place. A drawback to this approach is that when the cutter is to be moved to the next cutting location, the operator may occasionally forget to release the brake. Consequently, the brake may tear up the liner, or a hose connected to the support structure to move the cutter may be damaged.
Another problem with the extended brake in the prior art is that because the force exerted by the brake(s) along the liner, enough force may not be applied to one location on the liner to hold the support structure in place. Consequently, the cutter may vibrate and travel during cutting operation resulting in an inaccurate cut.
Many of the prior art devices cause debris from the liner to fall downward on the cutter during operation. This debris may clog up the cutter's moving components. Further, the debris may become entrained in the cutter's blades themselves so as to increase the time to cut the hole. Further, the prior art devices only have a limited cutting surface. Thus, the time to cut the hole is increased.
When a cutting head cuts the liner it typically cuts in two directions. First the cutting head moves upward to form a hole in the liner. Then the cutting head moves downward to spread the hole. When the cutting head moves downward it may not exert enough force to expand the hole after punching through the liner.
Finally, when the prior art cutting devices are repositioned during cutting, the operator may not react quickly enough to the movement of the cutter head to stop the cutter's reposition. Consequently, if the cutter mechanism moves too fast, it may overshoot its mark and damage the conduit or liner. This damage may result in a leaky liner.